In recent years, as far as radiation therapy systems for cancer treatment are concerned, cancer treatment systems (particularly, referred to as particle beam therapy systems) utilizing a particle beam such as a proton or a heavy ion have been developed and constructed. As is well known, in comparison with a conventional radiation therapy utilizing an X-ray, a gamma ray, or the like, a particle beam therapy utilizing a particle beam enables intensive irradiation onto a cancer diseased site, i.e., a particle beam can be irradiated in a pin-point manner along the shape of the diseased site; therefore, treatment can be performed without providing any effect to normal cells.
In the case where irradiation onto a diseased site such as a lung or a liver accompanied by respiratory movement is implemented, there has been implemented respiration-synchronized irradiation in which by use of a respiration detection signal from a respiration detector, a charged particle beam is irradiated in synchronization with the respiration. For example, Patent Document 1 discloses a particle beam irradiation apparatus that generates a respiration gate signal for allowing launch of a charged particle beam, based on a body-surface position detected by a respiration detector, and controls a synchrotron and a beam transport apparatus, based on the respiration gate signal. Patent Document 2 discloses a radiation therapy system that is provided with two kinds of monitoring apparatuses, i.e., an external monitoring apparatus (X-ray fluoroscope) for monitoring respiratory signals such as a body deformation amount and a respiratory air amount that can be monitored from the outside of a body and an internal monitoring apparatus for monitoring a respiratory phase based on information about the position of a treatment target, a bone, the diaphragm, or a marker embedded in the body, and that photographs an X-ray fluoroscopic image in synchronization only with the respiratory phase necessary for respiration-synchronized irradiation so as to realize high-accuracy respiration-synchronized irradiation with a few X-ray exposure dose.
In particle beam therapy, it is important that regardless of whether or not respiration-synchronized irradiation is implemented, a particle beam is accurately irradiated onto a diseased site such as a cancer. Accordingly, when undergoing a particle beam therapy, the patient is fixed, by use of a fixing device or the like, on a treatment table (patient platform) in a treatment room (an irradiation room) so that his position does not shift. In order to accurately position a diseased site such as a cancer within a radiation irradiation range, the position of a patient is roughly set by use of a laser pointer or the like and then the diseased site of the patient is precisely positioned by use of an X-ray image or the like.
However, in order to accurately position a diseased site such as a lung or a liver accompanied by respiratory movement, it is required that based on consecutively photographed images outputted from an X-ray image-capturing device and respiratory waveforms outputted from a respiration detector, an X-ray image is obtained at a timing when the position of the respiratory-movement diseased site relatively stabilizes, for example, at a timing of expiration and is utilized for positioning.